The present invention relates to a refrigeration device for containers for industrial use with circulation/evaporation of a refrigerant liquid in a closed circuit, and a refrigeration process using this device.
The refrigeration device and process in accordance with the present invention provide several advantages in the operational cost, functionality and other aspects of a refrigeration technique when compared to prior art processes of refrigeration using a refrigerant liquid.
The basic procedure used in the prior art is to achieve refrigeration in containers for industrial use, e.g., tanks containing the product to be refrigerated, by pumping refrigerant liquids, e.g., ammonia, R12, R22, R502, to refrigeration covers, or refrigeration jackets, at an excessive pumping level and in a direction from the bottom of the cover to the top of the cover. However, the refrigerant liquid goes into the lower part of the cover and comes out through the upper part in the form of a vapor that is more liquid, i.e., moist. For each pressure applied in the cover, there is a corresponding temperature of the refrigerant liquid. This pressure is regulated by thermostatic valves, constant pressure or by both in combination.
When the refrigerant liquid proceeds upward along the cover under pressure, the liquid performs a heat exchange process with the product to be refrigerated so that evaporation occurs. Since the refrigerant liquid is typically pumped in excess, and possibly even continuously, into the container, there is refrigerant liquid and vapor from the refrigerant liquid inside the covers. The liquid will have bubbles that tend to form and go up along the walls of the container. It is a significant disadvantage that these bubbles agglutinate and, thus, isolate the walls of the refrigerant liquid causing a low efficiency in the heat exchange process.
Another disadvantage in this conventional prior art process is that with the covers flooded, the volume of refrigerant liquid present in the system is too high. This also causes significant problems since the heating of the refrigerant liquid generates high internal pressures in the covers due to the expansion of the liquid during the heating process. There is also a significant operational cost to keep a large volume of refrigerant liquid circulating in the refrigeration system.
Another disadvantage of this conventional prior art refrigeration process is the risk to the environment and to the operators involved in the steps of the process, since the process involves high pressures, large volumes of refrigerant liquid, and a significant degree of toxicity of the materials in the process.
In addition to these afore-mentioned disadvantages, the conventional process using excessive pumping of a refrigerant liquid presents certain cycles of work when a refrigerant liquid is not acceptable. In this case, the system is drained, which complicates the installation and operation of the covers.
When the covers have a relatively high height, e.g., large tanks, there are different operating temperatures at each height of the liquid column, resulting from the direct action of the static pressure of the column of the refrigerant liquid which increases the evaporation pressure of the system. In these cases, the covers are divided into sectors of predetermined heights which makes the cost of the installation extremely expensive since there are more covers, more tubes, more auxiliary equipment for the operational control and maintenance. The system for circulation of the refrigerant liquid becomes more complicated.
This division of the covers into distinct sectors is also applied in certain procedures when necessary to refrigerate just one particular zone, i.e., a first zone, and afterwards complementary zones. In this manner, during the filling with the product to refrigerated, just the lower tank zone is initially refrigerated. Thereafter, as the tank is subsequently filled, the immediate zones become refrigerated. It is apparent though, that the disadvantages mentioned above occur in this procedure as well.